Pneumatic rubber tires conventionally have sidewall components which are positioned between at least one bead region of the tire and the tread region of the tire. The tread component of the tire is designed to provide a running surface of the tire for ground-contacting purposes. A wheel-rim mounting surface is conventionally provided in the bead region of the tire which is designed contact a rigid metal rim onto which the tire is mounted to create a tire/wheel assembly.
The bead region of the tire normally includes a rubber encapsulated essentially inextensible bead composed of a bundle of wire cords. The bead region of the tire also normally includes at least one rubber component having a tire mounting surface, for example a chafer and/or toe guard component, of a rubber composition which is designed to be rim-contacting, and therefore a mounting surface of the tire. Such mounting surface rubber composition conventionally contains a significant rubber reinforcing carbon black content and is thereby relatively electrically conductive. Such tire bead region with associated rubber component(s) are well known to those having skill in such art.
The tire tread may be of a cap/base layered construction with the outer cap layer having a running surface of the tire designed to be ground-contacting. The tread base layer underlies and supports the outer tread cap layer and designed to be a transition between the outer tread cap layer and tire carcass plies or tire belt plies. Such tread base layer is conventionally of a rubber composition reinforced with a significant rubber reinforcing carbon black content to be relatively electrically conductive. Such tire tread cap/base construction is well known to those having skill in such art.
A tire may often contain a circumferential belt ply positioned between the tread base layer and the tire carcass plies. Such belt ply is normally composed of metal cords of twisted, or cabled, metal filaments wherein the metal cords are encompassed by a rubber composition (e.g. a rubber wire coat) which is reinforced with a significant rubber reinforcing carbon black content to be relatively electrically conductive. Such belt ply positioning and construction is well known to those having skill in such art.
The tire carcass itself is normally composed of one or more plies of cords encompassed by a rubber composition which usually contains only a more minimal rubber reinforcing carbon black content so that it is thereby relatively electrically nonconductive as compared to said bead region components, tire tread base layer and belt ply rubber. However, for this invention, the rubber composition for a carcass ply, if desired, may be provided as being electrically conductive by inclusion of a significant carbon black content. The carcass ply(ies) typically extend from bead-to-bead through a crown region of the tire. Such carcass ply(ies) construction of the tire is well known to those having skill in such art. The crown region of the tire is the portion of the tire which includes the portion of the tire carcass beneath the tire tread region as the carcass ply(ies) passes from one bead region to the other bead region of the tire as one having skill in such art would understand.
Conventionally, the outer visible rubber layer of the tire sidewalls is of a rubber composition which is reinforced with a significant rubber reinforcing carbon black content so it is relatively electrically conductive in a manner that a suitable path of least electrical resistance is thereby provided to promote dissipation of static electricity from the bead region of the tire (from its wheel-rim mounting surface rubber component) to the tread region with its running surface.
For some applications, however, it may be desired to reduce the carbon black content of the tire outer sidewall layer to, in turn, reduce its hysteresis and thereby make it less hysteretic. A lower hysteretic tire sidewall rubber layer promotes a lower rolling resistance and/or lower heat build up for the respective tire with an associated beneficial increase in fuel economy for an associated vehicle and/or durability of the tire itself. Typically, an increase in the rubber composition's rebound value is indicative of reduced hysteresis if the rubber composition. In practice, a reduction of the carbon black content of the sidewall rubber composition may be accomplished by replacing a portion of the carbon black amorphous silica reinforcement (e.g. a precipitated silica).
However, such reduction in carbon black content in the outer sidewall layer can also significantly reduce the electrical conductivity of the tire sidewall layer, particularly if the carbon black content is reduced below its percolation point, which, in turn, can result in significantly reducing or even eliminating the aforesaid path of suitable electrical conductivity between the tire's bead region and the tire's tread region.
In one aspect, it is desired to provide a tire having an outer, visible tire sidewall layer of a rubber composition having a relatively low carbon black content to an extent that the tire sidewall rubber layer is relatively electrically nonconductive.
For this invention, an electrically conductive cord is provided to provide a path of least electrical resistance between the tire bead region and tire tread region. The cord is provided as a metal filament spirally (helically) wound around a core of one or more organic filaments. The significance of using a spirally wound metal filament is to enable the relatively inextensible metal filament to be dynamically extended and flexed, because of its helically coiled configuration, during the working of the tire and to thereby reduce its fatigue. The organic fiber is used to provided a supporting core substrate for the helically wound metal filament. The electrically conductive cord may also be comprised of an electrically conductive metal filament, electrically conductive carbon fiber or their combination, spirally wound around a core of at least one organic filament.
In the description of this invention, the term “phr” relates to parts by weight of an ingredient per 100 parts by weight of rubber, unless otherwise indicated.
The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated. The terms “vulcanized” and “cured” are used interchangeably unless otherwise indicated. The terms “compound” and “rubber composition” may be used interchangeably unless indicated. The term “carbon black” is used to refer to rubber reinforcing carbon blacks unless otherwise indicated. Exemplary rubber reinforcing carbon blacks may be referred to, for example, in the Vanderbilt Rubber Handbook(1978) on Pages 414 through 417.